The present invention relates to a method and system for operating a power-producing machine at maximum output torque under varying operating conditions. The invention is particularly suitable for operating an internal combustion engine at maximum output torque by oscillating the setting of ignition timing on opposite sides of a reference setting.
In so far as the knocking and exhaust gas emission problems do not significantly affect engine performance, spark ignition timing is usually controlled in response to engine variables (such as engine crankshaft speed and intake vacuum) so that a maximum amount of torque is delivered and fuel consumption rate is kept at a minimum. However, due to the difficulties encountered in calibrating the engine to its particular operating characteristics during the manufacturing stage, spark ignition advance setting is not necessarily adjusted to an optimum value for that particular engine. Even if such calibration is successfully achieved, the operating characteristics of the engine tend to vary as a function of environmental conditions (temperature, altitude, etc.) and as a function of aging, and therefore, the particular spark ignition setting would cease to be the optimum setting.
Attempts have been made to overcome this problem. U.S. Pat. No. 3,142,967 granted to Paul H. Schweitzer discloses a spark ignition control system in which spark ignition timing is continuously dithered or oscillated to either side of a reference advance timing to detect the resultant variation in an engine output variable such as engine speed at two consecutive points in time. The reference advance timing is corrected in one way or another in response to the result of a comparison between the detected output engine variables. More specifically, if the engine speed variation in response to an ignition timing dithered in the direction of advance with respect to the reference timing, is greater than the engine speed variation in response to an ignition timing dithered in the direction of retard with respect to that reference, the reference setting is corrected toward the advance side by a predetermined amount. If the former is smaller than the latter, the correction is made in the opposite direction.
Since the engine output variable is sensed at two points in time, there are only two possible relations or "permutations" in which the detected output engine variables occur in the order of magnitude. Therefore, upon manual command acceleration or deceleration, the detected output engine variables do not serve as a valid indication for purposes of correcting the reference advance setting. Otherwise stated, the prior art method is incapable of discriminating the engine output power variations resulting from the manual command from those variations resulting from the constant oscillation of the input variable, or spark ignition setting.